Deposition apparatus and methods

ABSTRACT

A deposition apparatus ( 20 ) comprising: a chamber ( 22 ); a process gas source ( 62 ) coupled to the chamber; a vacuum pump ( 52 ) coupled to the chamber; at least two electron guns ( 26 ); one or more power supplies ( 30 ) coupled to the electron guns; a plurality of crucibles ( 32,33,34 ) positioned or positionable in an operative position within a field of view of at least one said electron gun; and a part holder ( 170 ) having at least one operative position for holding parts spaced above the crucibles by a standoff height H. The standoff height H is adjustable in a range including at least 22 inches.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.14/774,489, filed Sep. 10, 2015 and entitled “Deposition Apparatus andMethods” which is a 371 US national stage application ofPCT/2014/028489, filed Mar. 14, 2014, which claims benefit of U.S.Patent Application No. 61/800,727, filed Mar. 15, 2013, the disclosuresof which are incorporated by reference herein in their entireties as ifset forth at length.

BACKGROUND

The disclosure relates to deposition of aerospace coatings. Moreparticularly, the disclosure relates to electron beam physical vapordeposition (EB-PVD) of ceramic thermal barrier coatings (TBC).

The current state of the art thermal barrier coatings (TBC) are producedby EB-PVD with a line of sight deposition capability. Line-of-sightdeposition occurs with the process done in a vacuum chamber at absolutepressures varying from 1×10⁻⁴ to 1.5e⁻² Torr (0.013 to 2.0 Pa), asdisclosed in Rigney, et al., U.S. Pat. Nos. 6,342,278 and 6,447,854.Vacuum levels below 1.5e⁻² Torr (2.0 Pa) ensure robust and durableoperation of the electron beam guns. At these pressures, the mean freepaths of gas and vapor molecules in the vacuum chamber are at least aslong as the size of the chamber. Thus, on average, gas and vapormolecules travel from the vapor source to the part being coated withoutcolliding with other gas or vapor molecules. Thus, on average,depositing vapor molecule trajectories are straight lines, leading toline-of-sight deposition.

Because TBCs are critical to part life and operation, TBC thickness andcoat zones are an input factor in part design. Today turbine vanes aretypically manufactured as singlets to enable much more uniform TBCthickness to allow these parts to operate in higher temperatureenvironments. However, a doublet (or triplet, etc.) has advantages inminimizing leakage losses between parts. There have been problemsobtaining uniform coatings on areas of each doublet airfoil which becomeoccluded by the other during deposition (see, e.g., U.S. Pat. No.8,191,504 of Blankenship).

Similar TBC thickness issues occur on other parts as well includingturbine blades. Optimizing deposition for the airfoil of a turbine bladeresults in low thickness build on the platform region. Complexmanipulation today has improved the thickness distribution but anincrease in non-line-of-sight (NLOS) deposition is desired for thesecomponents as well.

Modifications to the EB-PVD process are known in the prior art thatenable NLOS deposition. The directed vapor deposition (DVD) processrelies on supersonic jets surrounding the vapor source to improve NLOSdeposition, as disclosed in U.S. Pat. No. 8,110,043 to Hass et al.

SUMMARY

One aspect of the disclosure involves a deposition apparatus comprising:a chamber; a process gas source coupled to the chamber; a vacuum pumpcoupled to the chamber; at least two electron guns; one or more powersupplies coupled to the electron guns; a plurality of cruciblespositioned or positionable in an operative position within a field ofview of at least one said electron gun; and a part holder having atleast one operative position for holding parts spaced above thecrucibles by a standoff height H. The standoff height H is adjustable ina range including at least 22 inches.

In one or more embodiments of any of the foregoing embodiments, aprocess gas inlet is located at the bottom of the coating chamber.

In one or more embodiments of any of the foregoing embodiments, therange includes 8 to 25 inches.

In one or more embodiments of any of the foregoing embodiments, therange includes 15 to 22 inches.

In one or more embodiments of any of the foregoing embodiments, the partholder is mounted to a retractable sting shaft.

In one or more embodiments of any of the foregoing embodiments, the partholder is a rake having a pair of arms and, along each arm, a pluralityof rotary part-holding stations.

In one or more embodiments of any of the foregoing embodiments: theplurality of crucibles comprises a first set of crucibles and a secondset of crucibles; and an actuator is coupled to the first and secondsets of crucibles to shift the first and second sets into and out of theoperative position.

In one or more embodiments of any of the foregoing embodiments: each ofthe plurality of crucibles has an associated ingot loader; and the ingotloaders of the first set are different from the ingot loaders of thesecond set; and the ingot loaders of the first set carry ingots ofdifferent composition than do the ingot loaders of the second set.

In one or more embodiments of any of the foregoing embodiments, thecrucibles contain a ceramic melt.

In one or more embodiments of any of the foregoing embodiments, one ormore of: a pump and flow controller feedback system is capable ofcontrolling the chamber pressure within +/−7% of setpoint pressure overthe full range of process gas flowrates from 100 sccm to 100 slm; thepower supply can be switched between operation in the range 20-40 kV tooperating in the range 41-80 kV, with no change in power delivered tothe coating chamber.

In one or more embodiments of any of the foregoing embodiments, a methodfor using the apparatus comprises: controlling the process gas sourceand the vacuum pump to maintain an atmosphere of 3-30 Pa absolutepressure; and controlling the electron guns and power supplies to 20 to90 kV at 160-300 kW per gun.

In one or more embodiments of any of the foregoing embodiments: the partholder holds a plurality of vane doublets, each comprising an inboardshroud and an outboard shroud and a pair of airfoils therebetween; andparts are rotated around their radial axis at a constant rotation ratefrom 4 to 120 rpm, while simultaneously being tilted over a range from−45 to +45 degrees.

In one or more embodiments of any of the foregoing embodiments, the partholder holds a plurality of blades, each comprising: an airfoil having asubstrate having a leading edge, a trailing edge, a pressure side, and asuction side and extending from an inboard end to a tip; and anattachment root; and parts are rotated around their radial axis at aconstant rotation rate from 4 to 120 rpm, while simultaneously beingtilted over a range from −45 to +45 degrees.

Another aspect of the disclosure involves a method for operating adeposition apparatus, the deposition apparatus comprising: a chamber; aprocess gas source coupled to the chamber; a vacuum pump coupled to thechamber; at least two electron guns; one or more power supplies coupledto the electron guns; a plurality of crucibles positioned orpositionable in an operative position within a field of view of at leastone said electron gun; and a part holder having at least one operativeposition for holding parts spaced above the crucibles by a standoffheight H. The method comprises: adjusting the standoff height H to avalue in the range of 8 to 25 inches; controlling the process gas sourceand the vacuum pump to maintain an atmosphere of 3.0-30 Pa absolutepressure; and controlling the electron guns and power supplies to 20 kVto 90 kV at 160-300 kW per gun.

In one or more embodiments of any of the foregoing embodiments, theabsolute pressure is 6.6 Pa to 30 Pa.

In one or more embodiments of any of the foregoing embodiments, H is ina range of 15 inches to 25 inches

In one or more embodiments of any of the foregoing embodiments, themethod comprises: adjusting the standoff height H to a value in therange of 8 to 18 inches; controlling the process gas source and thevacuum pump to maintain an atmosphere of at most 2.0 Pa absolutepressure.

In one or more embodiments of any of the foregoing embodiments, thecontrolling of the process gas source results in flowrates 3 to 100 slm.

In one or more embodiments of any of the foregoing embodiments, thecontrolling of the process gas source results in flowrates 3 to 40 slm.

In one or more embodiments of any of the foregoing embodiments, thecontrolling the electron guns and power supplies is to a power of 120 kWto 300 kW per gun.

In one or more embodiments of any of the foregoing embodiments, thecontrol is such that a thickness ratio deposited on a flat plate heldstationary above the crucibles at any point, x, y, z can be approximatedby the equation:Thickness/Max Thickness=cos^(n)(θ₂)+cos^(n)(θ₂)+cos^(n)(θ₃), where nranges from 5 to 25

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a deposition apparatus.

FIGS. 2A and 2B are schematic end views showing rake arms tilted up anddown as parts continuously rotate to ensure uniform coating thicknessand microstructure on both the airfoil and platform.

FIGS. 3A and 3B are schematic end views showing an alternate rake armtilting configuration typically used with continuously rotating vanes toensure uniform coating thickness and microstructure on both the airfoiland both platforms.

FIGS. 4-1, 4-2, and 4-3 are a sequence of plan views showing shifting ofan ingot assembly relative to electron beam sources and parts.

FIG. 5 is a schematic diagram of an exemplary stepped flange design usedfor welded and vacuum-sealed flanges for containment of high energyx-rays produced by interaction of high energy electrons with material inthe coating chamber.

FIG. 6 is a schematic view of an electron beam gun of the system of FIG.1.

FIG. 7 is a side schematic view of the apparatus.

FIG. 8 is a side dimensional view of the positions of coating stationson a rake relative to deposition sources.

FIG. 9 is a plan view of the rake and sources of FIG. 5.

FIG. 10 is a plan view of an exemplary mechanical pumpset, pumpingmanifold, and chamber valve.

FIGS. 11 and 12 show a frame of reference.

FIGS. 13A and 13B are schematic plots depicting the change in vaporplume dimensions between conventional EB-PVD and low vacuum EB-PVD.

FIG. 14 is a plan plot of predicted coating thickness ratio on a planein the coating chamber above the ingots and parallel to the ingotsurfaces.

FIG. 15 is a schematic plan view of an ingot loader system.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 is a partially schematic plan view of a deposition system 20.Coating chamber 22 is shown without moveable load lock chambers and gatevalves between the preheat chambers and moveable load lock chambers.Additionally, the pumpsets for the preheat chambers and loadlockchambers are not shown. The chamber has an interior 24 which containsthe parts to be coated in an operative position during deposition. Thesystem further includes a pair of electron guns 26A, 26B (collectively26). The exemplary electron guns are positioned next to respective firstand second longitudinal ends 28A, 28B of the chamber. A power supply isprovided to power the guns. The exemplary power supply comprisesrespective power supplies 30A, 30B for the respective guns.

A source of deposition material comprises crucibles for melting ingotsof ceramic. As is discussed further below, the exemplary systemcomprises two sets of crucibles: a first set 32A, 33A, 34A, and a secondset, 32B, 33B, 34B. Each of the crucibles 32A, 33A, 34A, contains aningot/melt pool (atop the ingot) 36A of a first material while each ofthe crucibles 32B, 33B, 34B contain an ingot/melt pool 36B of a secondmaterial. The crucibles are part of an assembly 40 mounted forbidirectional movement in a direction 510 (e.g., via an actuator (notshown)) to alternatingly bring each of the two sets of crucibles into anoperative position where each crucible in that set is within the fieldof view (the beam scanning range) of at least one of the electron guns.In the exemplary FIG. 1 situation, the first set 32A, 33A, 34A is in theoperative position while the second set is laterally spaced apart. Thisenables multilayer ceramic TBC coatings. The exemplary first layerconsists of 6-8 wt % Y₂O₃, 92-94% ZrO₂. The exemplary second layerconsists of 53-65 wt % Gd₂O₃, 35 to 47 wt % ZrO₂. In other embodiments,even more layers can be created, by transitioning the ingots back andforth any number of times. Other variations may add a third or furthercrucible set (e.g., for depositing a yet different material).

The assembly 40 may further include an optional gravel tray 42surrounding the crucibles for rastering by the electron beams to controlpart temperature. The assembly 40 may further include loaders for eachof the crucibles (not shown). An exemplary loader contains multipleingots so as to be able to feed one ingot while storing one or moreother ingots and, thereafter, deliver the stored ingot to the crucibleto replenish. The loaders may be rotary cassette loaders (FIG. 15) orlinear magazines.

FIG. 1 further shows an optional shroud or radiative heat reflector 44positioned above the crucibles in the operative position (moreparticularly, above the parts in their operative position).

FIG. 1 further shows an exemplary load of six parts in the operativeposition. The six parts are arranged on part holders formed by two rakearms 170A, 170B (collectively or individually 170), three parts per rakearm. The parts attached via tooling (not shown) to rotating shafts thatare driven by crown gears (not shown) within the rake arms (180A, 180B).The rake arms are each attached to an associated triaxial sting shaft172, partially drawn in FIG. 1. The exemplary sting shaft consists ofthree coaxial shafts—only the outermost shaft is shown. The innermostshaft drives the crown gears that rotate the parts approximately aroundtheir longitudinal axes. A second coaxial shaft (not shown) is attachedto one rake arm 180A, allowing that rake arm to be rotated around theaxis of the sting shaft. The outermost coaxial shaft (shown) is attachedto the other rake arm 180B, allowing that rake arm to be rotated aroundthe axis of the sting shaft. Each shaft is driven by independent motors(not shown), allowing for independent rotation of parts around theirapproximate longitudinal axis and rotation of the rake arms around thesting shaft axis. This arrangement optimizes manipulation of parts toproduce uniform coatings.

FIGS. 2A and 2B show schematic examples of rake arm manipulation asparts are coated. As drawn, rake arms alternately rotate to an exemplary30 degrees above and below the horizontal. Parts are continuously orvariably rotated as the rakes are tilted. Rotation may also beperiodically stopped (e.g., for brief dwell intervals to achieve desireddeposition distribution). This ensures uniform coating thickness andmicrostructure on both airfoil and platform surfaces. An alternateconfiguration for rake arm manipulation is shown in FIGS. 3A and 3B. Onerake arm is rotated up while the other is rotated down. Thisconfiguration is typically used to coat vanes, to ensure uniform coatingthickness and microstructure on both airfoil and platform surfaces.

FIG. 1, further shows a pumping system 50 coupled to the chamber. Theexemplary pumping system comprises one or more pumps 52 (e.g., afrequency controlled variable pumping speed mechanical pump set). Adiffusion pump (not shown-hidden under the isolation valve 54) pumps thechamber down to a high vacuum and can be kept open for conventionalEB-PVD. The diffusion pump, however, is valved off for low vacuum EB-PVDso that the mechanical pumpset then does the pumping. The pumps arecoupled to the chamber via an exemplary valve system including aproximal high vacuum valve 54 and a mechanical pumpset isolation valve56 between the plenum and pump 52. The FIG. 1 pumps 52 are off the shelfitems, but the optimum combination and sizing of blowers and backingmechanical pumps, with pumping speeds controlled by variable frequencymotors, may be tailored for any particular application with the optimumsizing and combination of pumps in the pumpset based on specified flowrates and pressures to be used in operation.

A process gas supply system 60 comprises sources of one or more gases.An exemplary system 60 includes a supply 62A of oxygen (e.g., a tank orgroup thereof) and a supply 62B of argon (e.g., a tank or groupthereof). There may be multiple ways of delivering gases from thesources to the chamber either separately or together. The exemplarysystem 60 has both sources feeding a common supply trunk 66 (with flowscontrolled by individual valves 64A and 64B). The exemplary trunkbranches into separate branches 68 and 74 respectively delivering highmass flow rates and low mass flow rates. The branches 68 and 70 extendto the chamber and each includes an associated flow controller 72 and 74and valves (unnumbered) on either side of each flow controller. Theprocess gas supply system is discussed in more detail below.

There are gate valves 162, 166 shown in FIG. 1 on either side of thecoating chamber. These valves isolate the coating chamber from preheatchambers 160, 164 on either side of the coater—partially drawn inFIG. 1. These preheat chambers contain heating elements surrounded byheat shields (neither shown), which heat the parts to temperatures of1800° F. to 2000° F. (982° C. to 1093° C.), more particularly, 1800° F.to 1900° F. (1038° C. to 1093° C.), prior to coating. Mechanical anddiffusion pumping systems (neither drawn in FIG. 1) are also plumbed tothe preheat chambers. A partial second set of parts on rake arms ispartially shown in the operative preheat position on the right side ofFIG. 1. To maximize throughput, preheat and coating operations aresynchronized to ensure that once parts are coated and retracted from oneside of the coater, another set of parts is brought in to be coated onthe other side of the coater.

FIGS. 4-1 and 4-3 show a sequence of shifts of the assembly 40 betweenthe initial position wherein the first set of crucibles are in theoperative position (FIG. 4-1) through a third condition wherein thesecond set of crucibles is in the operative position (FIG. 4-3). In theintermediate condition of FIG. 4-2, an empty area between the ingot setsis in the operative position. However, the spacing between ingot sets issuch that, at this condition, all the crucibles are within the field ofview of at least one of the EB guns so that the gun may immediately jumpfrom heating crucibles of the first set to heating crucibles of thesecond set without having to wait. During transition, the controller maybe configured to expand the raster pattern of the guns to heat thesecond set of ingots while continuing to melt the first set of ingotsthat are initially in the operative position until a specific point intime where the raster patterns change to the other set.

The vacuum chamber may be of existing configuration or modified (e.g.,for improved robustness). With the EB guns operating at approximatelytwice typical voltages used in EB-PVD coaters, the chamber may be mademore robust to handle the higher intensity/higher energy x-raysassociated with the higher voltage. This may include providing thickerwalls and adding stepped flanges to ensure x-ray containment. Anexemplary stepped flange design is shown schematically exploded in FIG.5.

Each exemplary power supply is capable of high voltage operation.However, they may be configured for a diverse range which may allowswitching between a low vacuum and high voltage operating mode and ahigh vacuum and low voltage operating mode. Exemplary low vacuum modesin the vacuum level range 0.05 to 0.225 Torr (6.6 to 30 Pa), wouldrequire accelerating voltages above 30 kV and as high as 80 kV, orapproximately twice state of the art accelerating voltage. Acceleratingvoltages ranging from 20 to 40 kV are used for prior art conventionalEB-PVD (e.g., 1×10⁻⁴ to 0.015 Torr (0.013 to 2.0 Pa) vacuum levels).

FIG. 6 shows the EB guns as three-stage electron beam guns capable ofoperation at low vacuum. Each gun includes two stages 90, 92 pumped byturbomolecular pumps 94, 96 coupled to a remote mechanical pumpset at100. The first stage 90 is formed by a cathode chamber. The second stage92 is formed by an intermediate chamber. The third stage 98 is formed bya roughing chamber. The exemplary roughing chamber is separated from theintermediate chamber by an isolation valve 120. The exemplary roughingchamber is also coupled to the remote mechanical pumpset at 100. Theexemplary electron beam 500 exits the roughing chamber. Within and atthe top of the roughing chamber is a magnetic deflection coil that isdriven by the control system to raster the electron beam over a patterncontrolled by an external beam control system that is not shown. Highfrequency operation of the raster pattern is necessary to ensure uniformmelting of the ingots in the crucible, especially when raster patternsare used to melt more than one ingot at a time.

The exemplary electron beam guns are capable of operation when coatingchamber vacuum levels are as low (high numerically) as 0.225 Torr (30Pa). Precise magnetic optics and feedback circuitry and logic (notshown) produce very tightly focused electron beams with small beamdiameters, well centered in the gun's beam column. This enablesminimization of the orifice diameters for the beam column, thus reducingthe flux of gas and vapor from the coating chamber into the electronbeam gun, for a given chamber pressure. High vacuum inside the gun isrequired, since gun components operate at high temperatures, and wouldrapidly oxidize at lower vacuum levels.

High accelerating voltage is required to accelerate electronssufficiently for them to reach the melt pool without being scattered bybackground gases. The exemplary guns also use much higher frequencyrastering than is used in current state of the art coaters. Thisfacilitates evaporating two ingots with one gun (either when a given gunis used to heat both one of the peripheral ingots in the set and thecenter ingot or when the gun is used to switch between ingots of the twosets during the transition (e.g., to provide a graded compositiontransitioning between the two materials)).

Hardware components (e.g., the cathode plug and the anode ring assembly(not shown)) in the electron beam gun (not shown) may be changeable froma first set for low vacuum/high voltage operation to a second set forhigh vacuum/low voltage operation. The isolation valve 120 facilitatesreplacing of either of these. For example, the cathode plug assembly mayalso need to be replaced when the filament fails.

FIG. 7 shows the thermal hood 44 attached to an actuator 140 (e.g., apneumatic cylinder) that enables it to be raised and lowered. Thethermal hood serves to radiate heat back to the parts being coated.Adjusting the height of the thermal hood adjusts the temperature of theparts while they are coated. Part temperature during coating is a keyfactor for coating quality. An exemplary hood is flat or approximatelysemi-cylindrical and formed of a metal that may be water-cooled. FIG. 7further shows the optional gravel tray 42. The exemplary gravel tray isa water-cooled metal tray that is filled with zirconia gravel. Theelectron beam raster pattern is adjusted to heat the gravel withoutmelting it to provide radiative heat to the parts to maintain optimumpart temperature during coating. A high raster frequency increasescapability to fine-tune temperature control.

Each exemplary crucible is a water cooled copper crucible into whichceramic ingots are fed at a constant rate using a pusher rod. Theelectron beam melts the ingots, producing a melt pool that is containedby the crucible.

Previously noted, FIG. 1 schematically shows the tops of the ingots (ormelt pool when in operation) consisting of a ceramic composition. Onlyone row of two or three ingots is evaporated at a time. This enablesmultilayer ceramic TBC coatings. To transition from one layer toanother, the entire ingot assembly (all six crucibles and the feeders)is moved to position the other row of crucibles at the centerline of thecoater. During the movement of the ingots, the electron beam rasterpatterns are programmed to move at the same rate, maintainingevaporation during this transition. When the midpoint between the rowsof crucibles is situated at the chamber centerline, the electron beamraster patterns may be programmed to jump over to the other set ofingots, to start to deposit the 2^(nd) layer of ceramic coating, whichconsists of a different chemistry. Alternatively, the electron beamraster pattern may be programmed to start to heat the second set ofingots for a brief interval (e.g., three seconds to 100 seconds) beforejumping over to the second set of ingots and operating at sufficientpower/temperature to deposit from the second set. The exemplary firstlayer consists of 6-8 wt % Y₂O₃, 92-94% ZrO₂. The exemplary second layerconsists of 53-65 wt % Gd₂O₃, 35 to 47 wt % ZrO₂. In other embodiments,even more layers can be created, by transitioning the ingots back andforth any number of times, or by adding additional rows of ingots.

The FIG. 1 pumps 52 are off the shelf items, but the optimum combinationand sizing of blowers and backing screw pumps, with pumping speedscontrolled by variable frequency motors, may be tailored for anyparticular application with the optimum sizing and combination of pumpsin the pumpset based on specified flow rates and pressures to be used inoperation.

FIG. 7 further shows the preheat chamber 160 to one side of the mainchamber 22 separated by a gate valve 162. Along the opposite side, FIG.7 shows a second preheat chamber 164 separated from the chamber 22 by agate valve 166. The coating chamber is fed by two preheat chambers (oneon each side) such that as one set of part is heated, another set isgetting coated—the intent is to start melting, then continuously coatparts for a campaign lasting several days, at which point the coater hasto be cleaned and the guns rebuilt. FIG. 7 further shows the rake armassembly having a sting shaft 172 coupled to an actuator (not shown) forbidirectional motion in a direction 532 parallel to a central axis 530of the sting shaft. The sting shaft 172 extends through the preheatchamber and load chamber (not shown) and ends in the sting shaft chamber(not shown).

FIG. 7 is a side view showing one of the two rake arms 180 coupled tothe shaft 172. At a plurality of locations spaced along the arm, the armhas individual stations for engaging individual parts to be coated.Exemplary stations 184 are a crown bearing assembly that engages ageared shaft (not shown) inside the rake arm to drive rotation of thepart about an associated axis 550 of the station. Exemplary stations mayinclude a fixture portion complementary to some location on the part forgripping the part. In operation, exemplary part rotation rates are 5-100rpm, more particularly, 40-80 rpm for EB-PVD done at vacuum levelsranging from 0.05 Torr to 0.225 Torr (6.6 Pa to 30 Pa). Alternativelower ends to the pressure range are 3.0 Pa, 4.0 Pa and 5.0 Pa.Exemplary part rotation rates for prior art conventional EB-PVD (withvacuum levels ranging from 0.0001 to 0.015 Torr (0.013 to 2.0 Pa)) rangefrom 5 to 30 rpm.

FIG. 7 also schematically shows ingot feeder and crucible assembly 190.The ingot loaders and crucibles and gravel tray are vertically movablebidirectionally in a direction 560 by means of a vertical actuator (notshown). The entire crucible and feeder assembly is vertically adjusted(at the same time) to adjust standoff distance. The exemplary actuatorand system and entirely within the vacuum chamber although shownprotruding below for ease of reference. Such a configuration maintainsvacuum during operation (i.e., avoids leaks) but requires a fullbreaking of the vacuum to adjust position. The actuator may be automatic(e.g., hydraulic pneumatic or motor operated) or may be manual (e.g., amanual jack). The vertical adjustment allows control over standoffdistances between the melt pool surface and the parts. The standoffdistance may be characterized as the distance between the sting shaftcenterline and the plane of the meltpool surfaces or the rims ofcrucibles which may be just slightly higher. An exemplary range ofstandoff distance includes a range of between 8 and 25 inches (20 and 64cm). This may be slightly higher than baseline distances of which anexample is an 8-16 inches (20-41 cm) adjustment range. Thus, theexemplary system offers an adjustment to at least extend standoffdistance to 23 inches (58 cm), more particularly, 24 inches (61 cm) orat least 25 inches (64 cm) and more particularly with a range of atleast 15-25 inches (38-64 cm) for the low vacuum operation or 8-25inches (20-64 cm) to contemplate two modes of operation as discussedabove.

FIGS. 8 and 9 show two views of a two armed rake assembly wherein eacharm has five stations. The rake arm is shown in the operative position,over an exemplary three crucible set. The exemplary stations are formedin opposed pairs that equal longitudinal position. Each of these fiveexemplary pairs is evenly spaced from the adjacent pair(s). The locationof the extreme pairs of part stations are shown between the center andextreme ingot pairs—not outside of them, because the most uniformdeposition zone occurs over that area, especially for low vacuumdeposition up to 0.225 Torr (30 Pa).

Blades are typically held by the blade root—one blade per part station.The midspan of the airfoil may then be located above the centerline ofthe sting shaft. Then the rake arm is rotated such that the part tilts+/−30 degrees (more broadly, +/−10° to 45°) around an axis roughlythrough the midspan of the blade airfoil. Dwells at the extremes orhorizontal position of the tilting range may be used for tens ofseconds.

Vanes may be manipulated the same way as blades.

Alternatively, vanes may be attached to part stations on both rakes (atthe same time), such that again the tilt axis is through the midspan ofthe vane airfoil. In this arrangement, the vanes may be tilted similarlyto the blades. In this case, the rake arm motion is different than whenthe part is attached to only one rake. During tilting of parts attachedto only one rake, the rake arm motion is analogous to flapping wings.When parts are attached to two rake arms, the tilt motion of the rakearms is similar to a seesaw motion.

One may also run vanes such that two vanes in a row are fixture suchthat the fixture is attached to both rakes. In this case, the tilt axiswill run at the midpoint between the vanes, and the seesaw motion may beused.

One or more of several factors (e.g., modifications to baseline processand apparatus) may be utilized to improve NLOS deposition of TBCs.

TBC deposition at lower vacuum levels (e.g., up to 0.225 Torr (30 Pa),more particularly exemplary ranges of 0.05 to 0.225 Torr (6.6 to 30 Pa)or 0.1 to 0.225 Torr (13.3 to 30 Pa)) increase vapor molecule collisionsin transit from the evaporation source to the part. This means that thevapor cloud produced will enable a higher degree of NLOS deposition thancurrent state of the art EB-PVD processing.

Low vacuum EB-PVD may require modification to the coating equipment toenable deposition at 0.225 Torr (30 Pa). This includes a gun systemcapable of evaporating ceramic at these low vacuum levels. The electronbeam guns in the exemplary embodiment will be set to a constantaccelerating voltage. To increase power delivered to the ingot and meltpool, the beam current will be increased. As chamber pressure increases(and vacuum level decreases) the number of molecules per unit volumeincreases, by definition. Thus, for a given gun accelerating voltage andbeam current, increasing the chamber pressure (and lowering the vacuumlevel) increases the probability for interaction between the electronsand the background gas molecules. The majority of gas-electroninteractions are near elastic, meaning that very little energy transferoccurs during the interaction. However, the trajectory of the electrons(and the molecules, but to a much lesser extent) is altered. Summingthis effect over the whole electron beam, the net effect of the elasticinteractions is beam broadening. This is problematic, since it limitsthe precision of control of heating and melting.

In addition, some inelastic interactions occur. In this case, much moreenergy transfer occurs during the interaction between the electron andthe molecule. These interactions typically scatter the electrons out ofthe beam, reducing the energy density in the beam, thus the evaporationrate and the deposition rate. As the pressure continues to increase (andvacuum level decreases), one eventually gets to the point where all ofthe electrons are inelastically scattered out of the beam—the beam iseliminated.

Higher accelerating voltage reduces the probability of interactionsoccurring between electrons and molecules.

For prior art EB-PVD, operating in the 0.0001 to 0.0015 Torr (0.013 to2.0 Pa) pressure range, accelerating voltages in the range of 20 to 40kV are used. For low vacuum EB-PVD, with pressure ranging from 0.05 to0.225 Torr (6.6 to 30 Pa), the exemplary gun can be switched betweenoperating ranges of 30-45 kV, preferably 40 kV and operating ranges of60 to 90 kV, preferably 80 kV. In both modes, the maximum powerdelivered will be the same. That maximum power will be in the range 120kW to 300 kW per gun.

A vacuum system is used for control of vacuum level. The exemplarysystem is able to control vacuum level over a wide range (0.0001 to0.225 Torr (0.013 to 30 Pa)), and will be able to handle a large rangeof process gas flowrates, maintaining control of vacuum level within+/−5%. The exemplary range of process gas flowrates is between 100standard cubic centimeters per minute (sccm) and 100 standard liters perminute (slm). This vacuum level control capability is provided by anexemplary system that consists of one to five Roots blowers 320 (FIG.10) that feed three mechanical pumps 322. Each of the blowers can beturned on or off, and the pumping speed for each blower that is on canbe varied by varying the frequency of the AC power that is running it.

The crucible arrangement may be modified to provide a more a uniformvapor cloud for deposition thickness control.

A conventional process gas flow system is used for control of coatpressure and refinement of the vapor cloud.

In an exemplary high pressure EB-PVD mode, when the parts come in fromthe right preheat chamber, the left gun melts both the leftmost andcenter crucibles, while the right gun melts the right crucible.Vice-versa when the parts come in from the left preheat chamber. Meltingmay be done with a wide variety of raster patterns. Typically a roundraster pattern may be used, with the amount of time the beam spends atthe OD of the pattern is programmed to be more than at the center of thecircle, to accommodate the heat loss into the water-cooled crucible.

The EB guns may operate at ˜80 KV (e.g., 40-80 kV compared to prior artEB-PVD operation at ˜20-40 kV) for better penetration of the higherpressure.

A high volume roughing pump system with high vacuum preheat system maybe provided.

Shortening of the crucible to crucible distance may enable a moreuniform distribution vapor cloud for coating multiple parts at a time.

An exemplary location for process gas inlet (outlet of the gas/inlet tothe chamber interior) is at the bottom of the coating chamber, towardthe center of the floor of the chamber, to maximize the distance betweenthe process gas inlet and the electron beam guns. Alternative exemplaryoutlets of the gas system into the chamber interior are on a manifoldlow along one or more of the side walls. For example, the vacuum outletfrom the chamber may be high along one wall (e.g., the rear) or alongthe top or the chamber near that wall while the gas outlets (inlets tothe chamber interior) are low along the opposite wall (e.g., the front).The gas is thus introduced remote from the crucibles and oriented so asto merely pressurize and not serve as a motive flow propelling vaportoward the substrates as in DVD. FIG. 4-3 shows a manifold 58 withoutlets 59 low along a front wall. Exemplary process gas flowrates atthese inlets would be in the range of 3 to 100 slm, more particularly,10 to 100 slm or 3 to 40 slm. Additionally, one or more process gasmanifolds may be located near the crucibles or near the parts. Exemplaryprocess gas flowrates through these manifolds may range from 100 to 1000sccm.

This may be distinct from: a) a gas manifold surrounding the ingotassembly, with a valve allowing the gas manifold to be closed off (asused in DVD); and b) a gas manifold located just below the lowestposition of the adjustable thermal hood with a valve allowing the gasmanifold to be closed off. Gas flowrate in both manifolds are anexemplary between 20 and 1000 sccm. Oxygen or oxygen/argon mixes may beflowed in these manifolds.

Several design factors may be used to optimize coater design for coatingthickness uniformity in the coating zone, optimal coatingmicrostructure, and optimal deposition rate based on an empirical modeldescribed below.

The exemplary implementation of the model defines the z-coordinate ofthe plane defined by the melt pool surfaces as z=0, with positive zvalues being above the crucibles. The point of intersection of thatplane with the front left corner of the coating chamber defines x=0 andy=0, as shown in FIG. 11. The standoff distance is then the distancebetween the plane at z=0 and the centerline of the sting shaft, as shownin FIG. 11.

For EB-PVD coaters, and other vapor deposition coaters, the thickness ofcoating deposited at any given point (x,y,z) on a flat plate is known tofollow the following functional form, assuming one vapor source (themelt pool in this case): Thickness/Max Thickness=cos^(n)(θ) where θrefers to the angle subtended by the line from the center point of thecircular ingot surface to the point in question and the line normal tothe circular ingot surface at its center point, as shown in FIG. 12.

For multiple ingot sources, the distributions are superimposed topredict the thickness. For the example of the three ingot sources shownin FIGS. 11 and 12, the thickness ratio at any point, x, y, z isThickness/Max Thickness=cos^(n)(θ₁)+cos^(n)(θ₂)+cos^(n)(θ₃). The valueof n may be determined empirically, by coating flat plates and fittingthe data to the above equation.

This approach is well documented in the literature. For EB-PVD ofthermal barrier coatings at conventional vacuum levels (0.0001 to 0.015Torr (0.013 to 2.0 Pa)), exemplary values of n typically range from 2 to5.

For low vacuum EB-PVD, the experiments described above were carried outand the data was fit to the above equation. It was surprisingly foundthat n varies in the range 20 to 25 when the vacuum level varies from0.05 to 0.1 torr (6.7 to 13 Pa), respectively. This is a significantlysteeper distribution than occurs in the known prior art.

This discovery proved that coating under low vacuum conditions resultsin narrower vapor plumes, which requires closer spacing of the cruciblesin the coating chamber. FIG. 13 shows a typical embodiment for prior artEB-PVD, showing relatively broad, overlapping vapor plumes produced overcrucibles spaced with a spacing of C. FIG. 13 shows that the narrowervapor plumes produced in low vacuum EB-PVD require closer cruciblespacing, C′, to overlap the plumes, to produce uniform coating thicknesson parts. Using the value of n determined in the experiment describedabove, the correct crucible spacing for low vacuum EB-PVD coating, C′,can be determined, using the equation above.

As a consequence of the focusing of the vapor plumes that occurs in lowvacuum EB-PVD, the coating deposition rate increases significantly.Deposition rates ranging from 0.0005 inch to 0.004 inch (0.013 mm to0.10 mm), more narrowly, 0.0005 inch to 0.003 inch (0.013 mm to 0.076mm) or, within that range 0.0005 inch to 0.001 inch (0.013 mm to 0.025mm) or 0.0005 inch to 0.002 inch (0.013 mm to 0.05 mm) or 0.0007 inch to0.002 inch (0.018 mm to 0.05 mm) or 0.0008 inch to 0.002 inch (0.02 mmto 0.05 mm) of coating thickness increase per minute were observedrepeatedly for low vacuum EB-PVD. Conventional prior art EB-PVD coatingdeposition rates are typically in the range of 0.0002 inch to 0.0004inch (0.005 mm to 0.010 mm) per minute.

Similarly, there may be an optimal range of standoff distances overwhich the coating zone is uniform. As the standoff distance increases,uniformity increases. However, both the deposition rate per unit area onthe part and the effectiveness of radiative heating of the parts by themelt pools and the gravel tray goes down as standoff distance increases.Using the above equation and empirical data has enabled a determinationoptimum standoff distance as a function of pressure: the range is from15 to 22 inches (38 to 56 cm) for low vacuum EB-PVD coating.

FIG. 14 is a plot of exemplary output from the empirical model describedabove for a vacuum level 0.1 Torr (13.3 Pa), three cruciblesequidistantly spaced on a line with a spacing of 240 mm. The model showsthe normalized thickness (Thickness/Max Thickness) as a function ofposition on the plane located at a standoff distance of 21 inches (53cm). Each contour represents a range of 5%. The z-axis, coming out ofthe page in FIG. 14, represents the normalized thickness. The roundedrectangle drawn over the contour plot shows the approximate size andlocation of the coating zone—in which uniformity of the coatingdeposition is sufficient to ensure process capability.

The use of “first”, “second”, and the like in the following claims isfor differentiation within the claim only and does not necessarilyindicate relative or absolute importance or temporal order. Similarly,the identification in a claim of one element as “first” (or the like)does not preclude such “first” element from identifying an element thatis referred to as “second” (or the like) in another claim or in thedescription.

Where a measure is given in English units followed by a parentheticalcontaining SI or other units, the parenthetical's units are a conversionand should not imply a degree of precision not found in the Englishunits.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenapplied to an existing basic blade configuration, details of suchconfiguration or its associated engine may influence details ofparticular implementations. Accordingly, other embodiments are withinthe scope of the following claims.

What is claimed is:
 1. A method for operating a deposition apparatus(20), the deposition apparatus comprising: a chamber (22); a process gassource (62) coupled to the chamber; a vacuum pump (52) coupled to thechamber; at least two electron guns (26); one or more power supplies(30) coupled to the electron guns; a plurality of crucibles (32,33,34)positioned or positionable in an operative position within a field ofview of at least one said electron gun and comprising a first set ofcrucibles and a second set of crucibles; and a part holder (170) havingat least one holder operative position for holding parts spaced abovethe crucibles, the method comprising: powering the electron guns togenerate respective electron beams; heating the first set of crucibleswith the electron guns to vaporize material from the first set ofcrucibles; shifting the first set out of the crucible operative positionand the second set into the crucible operative position, wherein in anintermediate condition an area between the first and second sets is inthe crucible operative position; and heating the second set of crucibleswith the electron guns to vaporize material from the second set ofcrucibles wherein: in the intermediate condition, the crucibles of thefirst set and the second set are within the field of view of at leastone of the electron guns and the gun jumps from heating crucibles of thefirst set to heating crucibles of the second set without having to wait.2. The method of claim 1 wherein: during a transition from heatingcrucibles of the first set to heating crucibles of the second set,beginning to heat the second set while continuing to heat the first setuntil a specific point in time.
 3. The method of claim 2 wherein: thetransition from heating crucibles of the first set to heating cruciblesof the second set comprises expanding raster patterns of the electronguns and then at the specific point in time contracting the rasterpatterns.
 4. The method of claim 1 wherein: the first and second setsrespectively comprise a first row and a second row; and the shifting isof the first row and second row as an assembly.
 5. The method of claim 1wherein: during the shifting, a raster pattern of the electron gunsinitially moves with the first set.
 6. The method of claim 1 wherein:during the shifting, a raster pattern of the electron guns initiallymoves with the first set and then expands to also heat the second setand then contracts to heat only the second set.
 7. The method of claim 1wherein: the first set and the second set have ingots of differentchemistries from each other.
 8. The method of claim 1 wherein: the partsare turbine engine blades or vanes.
 9. The method of claim 1 wherein:the materials of the first and second sets of crucibles are ceramics.10. The method of claim 1 wherein: the material of the first set ofcrucibles is a first ceramic; and the material of the second set ofcrucibles is a second ceramic different from the first ceramic.
 11. Amethod for operating a deposition apparatus (20), the depositionapparatus comprising: a chamber (22); a process gas source (62) coupledto the chamber; a vacuum pump (52) coupled to the chamber; at least twoelectron guns (26); one or more power supplies (30) coupled to theelectron guns; a plurality of crucibles (32,33,34) positioned orpositionable in an operative position within a field of view of at leastone said electron gun and comprising a first set of crucibles and asecond set of crucibles; and a part holder (170) having at least oneholder operative position for holding parts spaced above the crucibles,the method comprising: powering the electron guns to generate respectiveelectron beams; heating the first set of crucibles with the electronguns to vaporize material from the first set of crucibles; shifting thefirst set out of the crucible operative position and the second set intothe crucible operative position, wherein in an intermediate condition anarea between the first and second sets is in the crucible operativeposition; and heating the second set of crucibles with the electron gunsto vaporize material from the second set of crucibles, wherein in theoperative position, the part holder holds parts spaced above thecrucibles by a standoff height H, the method further comprising:adjusting the standoff height H to a value in the range of 8 to 25inches; controlling the process gas source and the vacuum pump tomaintain an atmosphere of 3.0-30 Pa absolute pressure; and controllingthe electron guns and power supplies to 20 kV to 90 kV at 160-300 kW pergun.
 12. The method of claim 11 wherein: the absolute pressure is 6.6 Pato 30 Pa.
 13. The method of claim 11 wherein: H is in a range of 15inches to 25 inches.
 14. The method of claim 13 wherein the operating isoperating in a first mode and further comprising operating in a secondmode by: adjusting the standoff height H to a value in the range of 8 to18 inches; controlling the process gas source and the vacuum pump tomaintain an atmosphere of at most 2.0 Pa absolute pressure.
 15. Themethod of claim 11 wherein: the controlling of the process gas sourceresults in flowrates 3 to 100 slm.
 16. The method of claim 11 wherein:the controlling of the process gas source results in flowrates 3 to 40slm.
 17. The method of claim 11 wherein the controlling the process gassource and the vacuum pump and the controlling the electron guns aresuch that: a thickness ratio deposited on a flat plate held stationaryabove the crucibles at any point, x, y, z can be approximated by theequation:Thickness/Max Thickness=cos^(n)(θ₂)+cos^(n)(θ₂)+cos^(n)(θ₃), where nranges from 5 to
 25. 18. A method for operating a deposition apparatus(20), the deposition apparatus comprising: a chamber (22); a process gassource (62) coupled to the chamber; a vacuum pump (52) coupled to thechamber; at least two electron guns (26); one or more power supplies(30) coupled to the electron guns; a plurality of crucibles (32,33,34)positioned or positionable in an operative position within a field ofview of at least one said electron gun and comprising a first set ofcrucibles and a second set of crucibles; and a part holder (170) havingat least one holder operative position for holding parts spaced abovethe crucibles, the method comprising: powering the electron guns togenerate respective electron beams; heating the first set of crucibleswith the electron guns to vaporize material from the first set ofcrucibles; shifting the first set out of the crucible operative positionand the second set into the crucible operative position, wherein in anintermediate condition an area between the first and second sets is inthe crucible operative position; and heating the second set of crucibleswith the electron guns to vaporize material from the second set ofcrucibles, wherein: during a transition from heating crucibles of thefirst set to heating crucibles of the second set, beginning to heat thesecond set while continuing to heat the first set until a specific pointin time; and the transition from heating crucibles of the first set toheating crucibles of the second set comprises expanding raster patternsof the electron guns and then at the specific point in time contractingthe raster patterns.
 19. The method of claim 18 wherein: during theshifting, the raster patterns of the electron guns initially move withthe first set.
 20. The method of claim 18 wherein: during the shifting,the raster patterns of the electron guns initially move with the firstset and then is followed by the expanding.